Solid state lighting devices such as, for example, light emitting diodes (LEDs) are used for a number of applications. One type of such solid state lighting device is disclosed in International Patent Application No. PCT/US03/14625, filed May 28, 2003, entitled High Efficiency Solid-State Light Source And Methods Of Use And Manufacture, the details of which are hereby incorporated by reference.
Arrays of light-emitting diodes (LEDs) are used for many purposes. For example, arrays of LEDs are sometimes used in conjunction with arrays of lenses. The lens arrays are used to collect and collimate the light from the array of LEDs. However, since the light from LEDs emits into a wide range of angles, there is often a need to collect the light and project it more usefully. For example, as seen in FIG. 1, an array 10 of such light sources 12, such as, for example, LEDs are sometimes used with an array of lenses 14. Such lens arrays 14 are typically mounted above the LED array 10 and are used to collect and collimate the light from the LED array 10. The simplest and most common lens shape has a spherical surface to it, as shown in FIG. 1. The problem with the configuration in FIG. 1 is that the spherical design of each lens 16 assumes that the LED 12 is a point source of light. However, in reality LEDs are not point sources of light. Rather, LEDs project distributed light in a wide range of angles.
FIG. 2 shows a more accurate depiction of light emitted from an LED array 18. FIG. 2 shows that LEDs 20 often emit light from their sides, in which case the light is distributed and each LED 20 actually looks more like two closely spaced sources of light, rather than a single point source. Therefore, for some types of light sources, a single spherical lens 22 is an inadequate optic because it does not adequately gather or collect the disparate light so that it is more usefully projected. This makes the simple plano-convex lens an inappropriate shape for efficiently collecting and directing the light from such LED sources. In order to adequately collect such disparate light, two or more lenses would be required for each light source or LED.
In order to overcome the above-described problems, some light sources include a focusing optic that has an aspherical surface to collect disparate light from a source. The configuration of the aspherical surface for any given application may be determined, for example, by using typical lens makers equations know to those skilled in the art. Thus, the optimal aspheric shape for a collimating optic used with a highly divergent source such as an LED may be calculated. Aspherical surfaces are a well-established means of collimating the light from highly divergent sources. However, aspherical optics are complex and often too expensive and/or require expensive tooling to be practical. Even spherical lens arrays can be too expensive to manufacture for some low-cost, high-volume applications.
Examples of these various means of collimating the light from and LED are found in the following U.S. patents to Marshall et al (U.S. Pat. No. 6,547,423), Wu (U.S. Pat. No. 6,502,956), and Suzuki (U.S. Pat. No. 6,330,017), the details of which are herein incorporated by reference.
What is needed is a low-cost optic for a highly distributed and divergent light source that collects the light so that it is projected in a concentrated beam.
Additionally, what is needed is a low-cost solution for approximating complex optical surfaces to give adequate collection efficiency for arrays of light sources for lighting (non-imaging) applications.